Subject: [PATCH v2] x86, 64bit: cleanup highmap tail near partial 2M range

1. should use _brk_end instead of &_end in mark_rodata_ro().
   _brk_end can move up to &_end, i.e. to __brk_limit.  It's safe to
   use _brk_end when mark_rodata_ro() is called because extend_brk()
   is gone already at that point.
2. [_brk_end, pm_end) page range is already converted mem. and
   is not wasted.
3. add cleanup_highmap_tail for [_brk_end, pm_end).

Kernel Layout:
[    0.000000]    .brk: [0x0437c000-0x043a1fff]

Actually used brk:
[    0.272959] memblock_reserve: [0x0000000437c000-0x00000004382fff] flags 0x0 BRK

Before patch:
---[ High Kernel Mapping ]---
...
0xffffffff83400000-0xffffffff84200000          14M     RW         PSE GLB NX pmd
0xffffffff84200000-0xffffffff843a2000        1672K     RW             GLB NX pte
0xffffffff843a2000-0xffffffff84400000         376K     RW             GLB x  pte
0xffffffff84400000-0xffffffffa0000000         444M                           pmd
After patch:
---[ High Kernel Mapping ]---
...
0xffffffff83400000-0xffffffff84200000          14M     RW         PSE GLB NX pmd
0xffffffff84200000-0xffffffff84383000        1548K     RW             GLB NX pte
0xffffffff84383000-0xffffffff84400000         500K                           pte
0xffffffff84400000-0xffffffffa0000000         444M                           pmd

-v2: according to tglx
 caculate the pmd postion instead of passing last_pmd.
 cleanup_highmap_tail could not have __init, as it is called in mark_rodata_ro
 and mark_rodata_ro is called after free_initmem.
 highmap_end_pfn should keep PMD_SIZE alignment on !CONFIG_DEBUG_RODATA

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 arch/x86/mm/init_64.c  |   22 +++++++++++++++++++++-
 arch/x86/mm/pageattr.c |    4 ++++
 2 files changed, 25 insertions(+), 1 deletion(-)

Index: linux-2.6/arch/x86/mm/init_64.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/init_64.c
+++ linux-2.6/arch/x86/mm/init_64.c
@@ -411,6 +411,23 @@ void __init cleanup_highmap(void)
 	}
 }
 
+static void cleanup_highmap_tail(unsigned long addr)
+{
+	int i;
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	pgd = pgd_offset_k(addr);
+	pud = (pud_t *)pgd_page_vaddr(*pgd) + pud_index(addr);
+	pmd = (pmd_t *)pud_page_vaddr(*pud) + pmd_index(addr);
+	pte = (pte_t *)pmd_page_vaddr(*pmd) + pte_index(addr);
+
+	for (i = pte_index(addr); i < PTRS_PER_PTE; i++, pte++)
+		set_pte(pte, __pte(0));
+}
+
 static unsigned long __meminit
 phys_pte_init(pte_t *pte_page, unsigned long addr, unsigned long end,
 	      pgprot_t prot)
@@ -1124,7 +1141,8 @@ void mark_rodata_ro(void)
 	unsigned long end = (unsigned long) &__end_rodata_hpage_align;
 	unsigned long text_end = PFN_ALIGN(&__stop___ex_table);
 	unsigned long rodata_end = PFN_ALIGN(&__end_rodata);
-	unsigned long all_end = PFN_ALIGN(&_end);
+	unsigned long all_end = PFN_ALIGN(_brk_end);
+	unsigned long pmd_end = roundup(all_end, PMD_SIZE);
 
 	printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
 	       (end - start) >> 10);
@@ -1137,6 +1155,8 @@ void mark_rodata_ro(void)
 	 * should also be not-executable.
 	 */
 	set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
+	if (all_end < pmd_end)
+		cleanup_highmap_tail(all_end);
 
 	rodata_test();
 
Index: linux-2.6/arch/x86/mm/pageattr.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/pageattr.c
+++ linux-2.6/arch/x86/mm/pageattr.c
@@ -100,7 +100,11 @@ static inline unsigned long highmap_star
 
 static inline unsigned long highmap_end_pfn(void)
 {
+#ifdef CONFIG_DEBUG_RODATA
+	return __pa_symbol(PFN_ALIGN(_brk_end)) >> PAGE_SHIFT;
+#else
 	return __pa_symbol(roundup(_brk_end, PMD_SIZE)) >> PAGE_SHIFT;
+#endif
 }
 
 #endif